Enzyme immunoassay of anti–human acetylcholine receptor autoantibodies in patients with myasthenia gravis reveals correlation with striational autoantibodies

Anti-acetylcholine receptor (AChR) autoantibodies are a marker of acquired myasthenia gravis (MG). Some of these antibodies cause muscle weakness. Striational autoantibodies (Str Ab) also are a marker of MG. They are most prevalent in older patients and patients with thymoma. Here we describe a reproducible enzyme immunoassay (AChR-EIA) for detecting antibodies reactive with human muscle AChR, using antigens concentrated on plastic by prior sequential application of a biotinylated carrier, avidin, and biotinylated monoclonal IgG against AChR. There was significant correlation between values for antibodies assayed by AChR-EIA and by immunoprecipitation of AChR complexed with ¹²⁵I-α-bungarotoxin. Unexpectedly, AChR-EIA and StrAb values also were significantly correlated. Further studies revealed a significant and unprecedented correlation for StrAb and AChR precipitating antibodies. A plausible explanation for these findings is that some StrAb may react with cytoskeletal proteins that associate and copurify with AChR. The AChR-EIA offers a nonradioactive method for detecting two autoantibodies that are relatively restricted to patients with acquired MG.